In the framework of the Italian Space Agency (ASI) Technological Developments aimed at the measurement of the
Cosmic Microwave Background (CMB) polarization, a method to define and characterize focal surfaces of millimeter
wave telescopes has been implemented in a software package named WaFER (Wave Front Error evaluatoR). The
purpose of this tool is to rapidly optimize and characterize wide focal planes providing valuable information to study and
optimize high performance telescope configurations. This method is based on the GRASP9 Multi-Reflector GTD for the
computation of the weighted wave front error and the software output is the 3D focal surface as the region that
minimizes this figure of merit, in terms of feed locations and orientations, for polarization measurements. In addition
WaFER provides the main descriptive parameters of the main beams iteratively calculated with the GRASP9 Physical
Optics, using the information derived for the evaluated focal surface. The method has been applied at several telescope
configurations and WaFER could be used to define the focal surface of any reflector antenna system that can be studied
with GRASP9. It can be used to characterize the main beam descriptive parameters also in terms of polarization
properties and straylight. Finally, an estimate of the computational time is reported for each computational step (focal
surface evaluation, main beam simulations, polarization alignment).

We discuss the design and expected performance of STRIP (STRatospheric Italian Polarimeter), an array of coherent receivers designed to fly on board the LSPE (Large Scale Polarization Explorer) balloon experiment. The STRIP focal plane array comprises 49 elements in Q band and 7 elements in W-band using cryogenic HEMT low noise amplifiers and high performance waveguide components. In operation, the array will be cooled to 20 K and placed in the focal plane of a ~0.6 meter telescope providing an angular resolution of ~1.5 degrees. The LSPE experiment aims at large scale, high sensitivity measurements of CMB polarization, with multi-frequency deep measurements to optimize component separation. The STRIP Q-band channel is crucial to accurately measure and remove the synchrotron polarized component, while the W-band channel, together with a bolometric channel at the same frequency, provides a crucial cross-check for systematic effects.

The LSPE is a balloon-borne mission aimed at measuring the polarization of the Cosmic Microwave Background (CMB)
at large angular scales, and in particular to constrain the curl component of CMB polarization (B-modes) produced by
tensor perturbations generated during cosmic inflation, in the very early universe. Its primary target is to improve the
limit on the ratio of tensor to scalar perturbations amplitudes down to r = 0.03, at 99.7% confidence. A second target is
to produce wide maps of foreground polarization generated in our Galaxy by synchrotron emission and interstellar dust
emission. These will be important to map Galactic magnetic fields and to study the properties of ionized gas and of
diffuse interstellar dust in our Galaxy. The mission is optimized for large angular scales, with coarse angular resolution
(around 1.5 degrees FWHM), and wide sky coverage (25% of the sky). The payload will fly in a circumpolar long
duration balloon mission during the polar night. Using the Earth as a giant solar shield, the instrument will spin in
azimuth, observing a large fraction of the northern sky. The payload will host two instruments. An array of coherent
polarimeters using cryogenic HEMT amplifiers will survey the sky at 43 and 90 GHz. An array of bolometric
polarimeters, using large throughput multi-mode bolometers and rotating Half Wave Plates (HWP), will survey the same
sky region in three bands at 95, 145 and 245 GHz. The wide frequency coverage will allow optimal control of the
polarized foregrounds, with comparable angular resolution at all frequencies.

The ESA Planck mission is the third generation (after COBE and WMAP) space experiment dedicated to the measurement
of the Cosmic Microwave Background (CMB) anisotropies. Planck will map the whole CMB sky using two instruments in
the focal plane of a 1.5 m off-axis aplanatic telescope. The High Frequency Instrument (HFI) is an array of 52 bolometers
in the frequency range 100-857 GHz, while the Low Frequency Instrument (LFI) is an array of 11 pseudo-correlation
radiometric receivers which continuously compare the sky signal with the reference signal of a blackbody at ~ 4.5 K.
The LFI has been tested and calibrated at different levels of integration, i.e. on the single units (feed-horns, OMTs, amplifiers,
waveguides, etc.), on each integrated Radiometric Chain Assembly (RCA) and finally on the complete instrument,
the Radiometric Array Assembly (RAA). In this paper we focus on some of the data analysis algorithms and methods that
have been implemented to estimate the instrument performance and calibration parameters.
The paper concludes with the discussion of a custom-designed software package (LIFE) that allows to access the
complex data structure produced by the instrument and to estimate the instrument performance and calibration parameters
via a fully graphical interface.

In this paper we present the test results of the qualification model (QM) of the LFI instrument, which is being
developed as part of the ESA Planck satellite. In particular we discuss the calibration plan which has defined
the main requirements of the radiometric tests and of the experimental setups. Then we describe how these
requirements have been implemented in the custom-developed cryo-facilities and present the main results. We
conclude with a discussion of the lessons learned for the testing of the LFI Flight Model (FM).

PLANCK is the space mission of the European Space Agency devoted to measure of the anisotropies of the cosmic microwave background (CMB), the relic radiation left by the big bang.
The satellite will be launched in 2007 and it will carry state-of-the-art of microwave radiometers and bolometers arranged in two instruments, respectively the Low Frequency Instrument and the High Frequency Instrument, both coupled with a 1.5 m telescope and working in nine frequency channels between 30 and 857 GHz.
From the second Lagrangian point of the Sun-Earth system, the instruments will produce a survey that will cover the whole sky with unprecedented combination of sensitivity, angular resolution, and frequency coverage, and they will likely lead us to extract all the cosmological information encoded in the CMB temperature anisotropies.
The development strategy of PLANCK and the two instruments has been to set up a mission that inherently minimizes the systematic effects.
The optics, composed by an optimised telescope-feed array assembly, introduce unwanted systematic effects in the measurements like the so called external straylight due to the sidelobe pick-up.
A trade-off between angular resolution and external straylight has been carried out for LFI in order to reach the best optical performances preventing the Galactic contamination. The main product of the study has been the definition of the internal geometry of the flight model of the LFI feed horns and the characterization of the overall optical response of the instrument.
Thermal emission from all components of the spacecraft produces the so called internal straylight, that has been evaluated and controlled in the design phase.
In this paper we present the study carried out on the minimization of straylight contamination in PLANCK LFI.

PLANCK represents the third generation of mm-wave instruments designed for space observations of Cosmic Microwave Background anisotropies within the new Cosmic Vision 2020 ESA Science Programme. The PLANCK survey will cover the whole sky with unprecedented sensitivity, angular resolution, and frequency coverage. The expected scientific return will be enormous, both for the cosmological constraints that will be set and for the gold mine of information contained in the astrophysical foregrounds. To reach these ambitious scientific goals, the control of systematic effects is mandatory and a careful instrument design is needed, as well as an accurate knowledge of instrumental characteristics. The Low Frequency Instrument (LFI), operating in the 30 ÷ 70 GHz range, is one of the two instruments onboard PLANCK Satellite, sharing the focal region of a 1.5 meter off-axis dual reflector telescope together with the High Frequency Instrument (HFI) operating at 100 ÷ 857 GHz. We present a detailed study carried out by the LFI team on the performances of the PLANCK telescope coupled with LFI feed horns, both in the main beam and in the sidelobe region.

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